Dust leak detector for air cleaner systems

ABSTRACT

Apparatus and method is disclosed for continuously sampling, at a point downstream of the air cleaner, the normally clean air entering an engine to produce a signal indicating the cleanliness of the total air stream entering the engine. A sample of the air is continuously circulated through a small detector filter and the resistance of the filter to air flow is continuously monitored. In case of dust leakage, the resistance of the detector filter increases very rapidly because of increased dust loading, giving an immediate indication of the abnormal condition.

United States Patent Johnson et al.

[54] DUST LEAK DETECTOR FOR AIR CLEANER SYSTEMS [72] Inventors: LemolneL. Johnson; William P. Timmons, both of Minneapolis, Minn.

[73] Assignee: Donaldson Company,

neapolis, Minn.

221 Filed: 0ct.15, 1969 211 Appl.No.: 870,458

Inc., Min- [52] US. Cl. ..73/1l8, 73/28, 73/38, 340/239 F [51] Int. Cl...G01m 15/06 [58] Field of Search ..73/28, 38, 196, 202, 118, 61;55/274; 340/239 [56] Relerences Cited UNITED STATES PATENTS 2/1911Touzalin ..73/28 4/1957 Salko et al. ..73I196 X 8/1959Becker...............73/42l.5 UX

[ 1 Oct. 10,1972

3,033,030 5/ 1962 Heller ..73/1 18 3,258,960 7/1966 Baden et al ..73/1183,352,197 11/1967 Forges et a] ..73I6l R UX FOREIGN PATENTS ORAPPLICATIONS 158,137 1/1964 U.S.S.R. ..73I28 Primary Examiner-Charles A.Ruehl Attorney-Merchant & Gould ABSTRACT Apparatus and method isdisclosed for continuously sampling, at a point downstream of the aircleaner, the normally clean air entering an engine to produce a signalindicating the cleanliness of the total air stream entering the engine.A sample of the air is continuously circulated through a small detectorfilter and the resistance of the filter to air flow is continuouslymonitored. In case of dust leakage, the resistance of the detectorfilter increases very rapidly because of increased dust loading, givingan immediate indication of the abnormal condition.

llclalm9DrawlngFlgures emu/term) Ell/61MB DUST LEAK DETECTOR FOR AIRCLEANER SYSTEMS BACKGROUND OF THE INVENTION amounts of dust in the airdownstream from an air m cleaner as an indication of leakage at somepoint in the clean air flow path.

2. Description of the Prior Art Present day engines operating in dustcontaminated environments require a continuous supply of clean air toavoid excessive engine wear and deterioration. Current practice is toprovide highly efficient air cleaner systems to remove dust and othercontaminants which otherwise would enter the engine via the intake air.These systems typically remove 99.99 percent of a standard test dustsuch as AC Coarse Test Dust for all ambient concentrations.

While present air cleaner systems provide adequate engine protectionunder almost all operating conditions, there is an inherent danger ofexcessive engine wear in the event of either a fracture in the filterelement media or a leak in the intake duct work between the air cleanerand the engine. Further, improper assembly of the filter element withinthe air cleaner can produce the same effects. When such events occur,there is usually no warning that the dust leak goes unnoticed untilsevere engine wear or even failure has resulted.

In order to protect against the effects of dust leaks occurring withinthe air cleaner itself, for example a fractured element or an elementimproperly installed, some air cleaner designs incorporate a secondaryor safety element. The safety element is simply another barrier-typefilter which operates in series with the primary element. These safetyelements have the disadvantage of increasing the air cleaner cost andsize. Moreover, safety elements are also subject to failure or improperinstallation and do not protect against dust leaks occurring between theair cleaner assembly and the engine.

SUMMARY OF THE INVENTION The present invention provides a means ofdetecting dust leaks occurring in an air cleaner or in the duct workleading to the engine. It also provides a warning signal such that thedust leak may be corrected before significant engine damage occurs. Thepresent invention provides apparatus and method for continuouslysampling the intake air stream at a point downstream of the air cleanerand for producing a continuous signal which indicates the cleanliness ofthe total air stream entering the engine.

A sample of the intake air stream is continuously circulated through adetector consisting of a small piece of suitable filter medium. Undernormal operating conditions with no dust leaks in the system, theresistance to flow offered by the filter detector will remain relativelyconstant. There will only be a small change in resistance because onlyvery small particles of dust are present downstream from the air cleanerand also because most of the fraction of dust that passes the primaryfilter will also pass the detector filter. During conditions of a dustleak, however, substantially larger dust particles will be present inthe intake air stream. In this situation. the resistance of the detectorelement will change very rapidly because of the increased dust loadingon the detector element. This change in resistance can be measureddirectly in terms of pressure drop change across the detector element.Depending upon the method of providing the sampling flow, andparticularly upon the total pressure drop or potential across thesampling circuit, the change in resistance across the detector elementcan result in output pressure drop signals of several inches of water.In general, the maximum output pressure drop signal that can be derivedis limited to the pressure drop across the sampling circuit. This wouldcorrespond to a condition where the detector element is completelyplugged because of the dust leak.

By using the present invention, excessive engine wear or failure causedby physical damage to the air cleaner system, can be avoided. Outinvention is simple and inexpensive to install and the detector elementcan be serviced at the same time the air cleaner itself is serviced.These and other advantages of the present invention will be more fullydescribed in the following specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of thedetector system as applied to carbureted engines;

FIG. 2 is a schematic diagram of the detector system as applied toturbo-charged or super-charged engines;

FIG. 3 is a schematic diagram of the detector system as applied tonaturally aspirated engines;

FIG. 4 is a schematic diagram of the detector system with a turbulenceamplifier providing the output signal;

FIG. 5 is a sectional view of a detector filter and the mountingassembly therefor;

FIG. 6 discloses schematically the use of a differential pressure switchto measure the resistance of the detector filter;

FIG. 7 is a schematic diagram showing the use of a pneumatic bridgecircuit to measure the resistance of the detector filter;

FIG. 8 is a graph showing particle size frequency versus particle sizeunder normal and abnormal intake air conditions; and

FIG. 9 is a series of three schematic diagrams showing the effect of airvelocities in the duct arid in the probe upon larger dust particles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 showschematically the application of the present invention to threedifferent types of engines. In each case, the engine is provided with anair cleaner and with suitable duct work leading from the air cleaner tothe engine. As shown schematically in FIG. I, the air cleaner maycomprise a cylindrical filter element 10 through which the air is drawn.The filter element can be constructed from a fibruous medium, pleated orotherwise, according to any present well known practice. The air cleanercould also comprise an inertial precleaner and a filter element inseries therewith. An oil bath air cleaner might also be used. Thepresent invention is not concerned with the type of air filter orcleaner that is used, so long as it provides a normally clean flow ofair through the duct work leading to the engine.

As shown schematically in FIG. 1, the sampling circuit includes a probe11 mounted in the air duct, inlet tubing 12 connected between the probe11 and the detector I3, and outlet tubing 14 connected between thedetector 13 and the intake manifold of the engine. With this arrangementof components in a carbureted engine, the potential or pressure dropacross the sampling circuit is approximately equal to the intakemanifold depression. This potential or pressure drop causes a suitableamount of clean" air from the air duct to be drawn or circulatedcontinuously through the detector 13. If the filter is damaged orimproperly installed, abnormal amounts of dust or dirt may pass throughthe air cleaner into the duct work leading to the engine. A portion ofthis abnormally dirty air will be drawn into the probe I1 and throughthe detector 13. When this occurs, a suitable output signal will beprovided in a manner later to be described.

FIG. 2 discloses the same type of detector system as applied to aturbo-charged or super-charged engine. In applications such as this,involving intake. air at pres sures above atmospheric pressure, thesampling circuit can be installed on the high pressure side of thecompressor. The sample flow may then be passed through the detector 13and discharged to atmosphere through a check valve 15 to prevent reverseflow through the detector.

In naturally aspirated engines, as shown in FIG. 3, there is not aconvenient potential or pressure drop source to provide sampling flow.In these applications the required sampling flow can be induced by meansof an ejector 16 that can be powered by either a compressed air sourceor exhaust gas energy. Again, a difference in pressure between the probe11 and the throat of the aspirator 16 provides the sampling flow throughthe detector 13.

FIGS. 4 and 7 disclose another approach to providing sampling flowpotential in any closed air flow system. This method involves creating achange in static pressure between two stations in the air duct by meansof varying the velocity of the air. An efficient and practical way toaccomplish this velocity change in the air duct is by means of a venturil7 installed in the air duct. The probe 11 is positioned upstream fromthe narrow throat portion of the venturi I7. Static pressure will alwaysbe lower at the throat portion of the venturi than at the probeentrance. Therefore, there will always be flow into the probe, throughthe detector and back to the primary flow at the throat of the venturi.As indicated above, a venturi can be installed in any closed air flowsystem to provide a pressure difference to establish air flow throughthe detector.

The construction of the detector 13 is shown in FIG. 5. Detector 13comprises a pair of housing portions 13a and 13b and a small filterelement 20. Housing portion 13b is provided at one end with a cavityinto which housing portion 13a snugly interfits. The two housingportions can be held together by a friction fit or suitable matingthreads can be provided. Both of the housing portions 130 and 13b areprovided with axial air passages 21 and 22 respectively, that arealigned with each other when the unit is assembled. Air passages 21 and22 increase in diameter toward the center of the assembled unit to formfrusto-conical shaped chambers on opposite sides of the filter element20. The outermost ends of the axial passages 21 and 22 are connected tothe inlet and outlet tubing I2 and I4 respectively.

In the preferred embodiment of our invention, the filter element 20 iscircular in shape and is positioned in a small circular cavity 23 formedin the end wall of the small housing portion 130, coaxial with passage21. When the unit is assembled, the edges of filter member 23 aregripped tightly between the two housing portions 13a and 13b so that thecenter portion of the filter member 20 extends across the axialpassageway 21-22. Therefore, all air passing through the detector 13must pass through the filter member 20.

The detector filter 20 can be a single flat sheet of filter mediumapproximately 1 inch in diameter. The exact size will depend upon thetype of material, the sampling flow rate, total pressure drop across thesampling circuit, and characteristics of the output or signal component.It is necessary that the detector filter 20 be of appropriate size toinsure proper sensitivity to dust loading. Further, the filter mediummust be selected such that the normally clean air flowing through thesampling circuit will not too rapidly change the fluid re sistance ofthe detector filter 20 with dirt and dust. The detector filter should besized and constructed from a material such that it can be cleaned orreplaced at the same time the primary air cleaner is serviced.

Again, the purpose of the detector is to continuously monitor a sampleof the normally clean air to detect the presence of abnormal amounts ofdirt or dust. When an abnormal condition occurs, the larger dustparticles will be filtered out of the sampling tream by the detectorfilter 20. Because of the relatively small size of the detector filter20, the buildup of dirt thereon will quickly increase its resistance toair flow. This increase in resistance to air flow of the detector filter20 is the parameter or variable that must be monitored to provide asuitable output signal from the system. The output device must bedesigned such that it is sensitive to the pressure drop which isproduced during abnormal leak conditions, but the relatively smallerchanges in pressure drop across the filter element that occur duringnormal operation must not produce the warning signal.

One type of output device is shown in FIG. 4. The sensing device can bea turbulence amplifier 25, with the sampling flow through the detector13 being used as a control input to the turbulence amplifier. With aclean air stream, there will be no significant change in the resistanceof detector 13 so that a control flow from outlet tubing 14 will becontinuously present as a control input to the turbulence amplifier.Under these conditions there will be no signal to the output device fromthe turbulence amplifier. When a dust leak occurs, the detector cellresistance will increase, reducing the control flow to the turbulenceamplifier. When the control flow is sufficiently reduced, the turbulenceamplifier will produce a signal to the output device. The details of theturbulence amplifier are not shown because devices of this kind arecommercially available.

Another method of monitoring the pressure drop across the detector 13 isshown in FIG. 6. A differential pressure switch 26 is connected bysuitable tubing to the inlet tubing 12 and the outlet tubing 14 asshown. Differential pressure switch 26 thus continuously monitors thepressure difference between the inlet and outlet of detector 13.Differential pressure switch 26 is set so that the normal pressure dropacross the detector 13 is below the switching point all during thenormal service life of the air cleaner system. Thus, normal changes inthe resistance of detector unit 13 will not cause the operation ofswitch 26. The switching point will be reached only if a dust leakoccurs causing a significant increase in the resistance of detectorelement 20. A suitable output device 27 is provided to give a warningsignal when switching occurs. Output device 27 can be a light, buzzer orother signal device.

Another approach to measuring the change in resistance of detector 13 isshown in FIG. 7. First of all, probe 11 is mounted in the air ductupstream of a venturi 17 into the throat of which is connected theoutlet tubing from the detector circuit, to provide the necessary airflow therethrough. In this approach, the detector 13 is mounted in apneumatic bridge circuit, forming a part of one leg thereof. The bridgecircuit has a first leg comprising a pair of known fluid resistor meansR2 and R3, and a second leg comprising the detector 13 (Rf) and anotherknown fluid resistor R]. A differential pressure device 26 is connectedbetween the center of the first leg, monitoring a static pressure Pa,and the center of the second leg, monitoring a static pressure Pb. Thetotal pressure in the duct surrounding probe 11 is indicated as Fe, andthe static pressure in the throat of the venturi 17, at the outlet ofthe detector circuit, is indicated as Pd.

Flow resistances R1, R2 and R3 are of a fixed type, either orifices ofsmall diameter sections or tubing. in the preferred embodiment of ourinvention, the known fluid resistors R1, R2 and R3 are capillary tubes.For capillary tubes, the fluid resistance R equals the pressure dropacross the tube (A P) divided by the flow rate (Q) and is constant forall Reynolds numbers below 2,000. This equation can be written R AP/Q.For a given resistance and capillary tube diameter the length of thetube can be detennined.

The initial or normal detector resistance is chosen so that the bridgecircuit is biased in the preferred direction. This will produce apressure drop potential across the differential pressure device 26.Under all normal operating conditions, the bias will remain in thispreferred direction because the detector resistance will remainessentially constant. As previously indicated, the resistance ofdetector 13 remains essentially constant for the service life of the aircleaner. However, under conditions for dust leak and increasingresistance of the detector 13, the bridge circuit will shift through thebalance or null point and establish a pressure drop bias in the oppositedirection. This change in the bias direction produces the necessarysignal to the output device 27.

In the preferred embodiment of our invention, the bridge is constructedso that the low pressure is initially in the known resistor leg (R2-R3)rather than the leg with the filter element. This is accomplished byproperly sizing the fixed resistances. Preferably, the switching pointof the bridge is set for the null or balance point of the bridge circuitwhere Pa equals Pb. Under normal conditions, Pb is greater than Pa.

For any given system, the initial pressure difference between Po and Pdwill be known. The initial amount of detector resistance at a given flowrate will also be known. The resistances R1, R2 and R3 are then selectedto obtain the proper flow rate through the legs of the bridge circuitwhile obtaining a suitable pressure difference between Pa and Pb. Again,under normal flow conditions, Pb should be greater than Pa. If theswitching point is then set for the null point of the bridge circuit,the detector is made insensitive to flow rate in the main duct. Thedetector can be made insensitive to flow rate in the main duct in thismanner because, even though the difference between Pc and Pd may changeradically with changes in air flow in the main duct, the balance pointof the bridge is always reached when the ratio of RflRl equals r3/r2. Ifthe switching point is set for other than the balance point of thebridge, the selected difference between Pa and Pb may occur at differentdust loading on detector 13, depending upon the flow rate through themain duct.

The following is an example of actual flow rates and pressure drops in abridge circuit we have built and tested. The designation Q1 refers tothe flow rate in the Rl-Rf leg of the bridge, while the designation Q2refers to the flow rate in the fixed or R2-R3 leg of the bridge.

1 R1 107.7 H20/CFM R3 227 H20ICFM in the above example, differentialpressure device 26 would be set to provide an output signal 27 when Pbminus Pa equals zero. Again, this occurs when the ratio Rf/Rl equalsR3/R2. By changing these variables, the required amount of dirt fed intothe main duct that will change Pb minus Pa to a zero value required forswitching can be changed. For examples, if more air flow through thedetector 13 is provided, it will load up faster when dirt is present. Achange in the flow rate would require changes in the other variables aswell. The sensitivity of the bridge circuit for any given detector 13and flow rate therethrough can be changed by changing the fixedresistances to provide a different normal pressure difference between Paand Pb. Generally speaking, the greater normal difference between Pa andPb, the more dirt loading will be required to cause the bridge circuitto reach the null point.

A preferred sampling technique has also been devised that will reducethe possibility of producing a spurious warning signal. After thefiltration process is completed, the air stream normally contains acertain number of particles that have passed through the filtrationsystem. For any given filtration system, these particles will have asize distribution that can be graphically portrayed. A graph for atypical system is shown in FIG. 8. The solid line of the graph is a plotof particle size frequency versus particle size under normal air flowconditions. It can be seen that relatively large numbers of smallerparticles are present but that relatively few larger particles arepresent. An abnormal condition, when a dust leak is present, is shown bythe dashed line. It can be seen that the particle size distribution ischanged and that there are greater numbers of larger particles.Therefore, in order to recognize this abnormal situation, the detectorsystem should discriminate in favor of recognizing increased numbers ofthe larger particles. The basic function of the dust leak detector is torecognize this condition of abnormal particle size distribution, andsignal when this condition occurs.

As shown in FIG. 9, the detector system can be biased toward recognizingthe larger or "abnormal" particles. Referring to FiG. 9, the probe 11 isshown under three different conditions of air stream velocity. In FIG.9(a) the velocity of the air stream through the probe is greater thanthe velocity of the air stream in the duct surrounding the probe. InFIG. 9(b) the two velocities are equal. In FIG. 9(c) the air velocity inthe duct is greater than the velocity of the air passing through theprobe. Most norma sized particles will follow the stream lines, shown asarrows in flG. 9. On the other hand, the larger or abnormal particlesbecause of their greater momentum, will continue along their normalpath. Therefore, the condition shown in FIG. 9(c) is used in leakdetection because many of the normal sized particles will follow thestream lines around the probe while the heavier particles follow theirnormal path into the probe. The condition of FIG. 9(c) is obtained bylimiting the air flow through the probe to less than the air fiow thatwould pass through an area equal to that of the probes inlet at thegiven stream velocity. By using the condition of FIG. 9(c), the detectorwill be responsive to an abnormal particle size distribution and will berelatively less responsive to the "normal" size distribution. Thus, thepossibility of producing a spurious warning signal is reduced by usingthe sampling condition shown in FIG. 9(c).

The present invention is applicable to all types of engines and can beinstalled in existing systems without increasing the size orconfiguration of the intake design. The system imposes no significantadditional intake loss on the engine. If the detector system isinstalled just ahead of the engine, it will protect against all intakeleaks and not just those occurring in the air cleaner itself. The systemcontinuously monitors the air stream and provides a warning signalshortly after a dust leak occurs, preferably at a location remote fromthe air cleaner itself and in view of the engine operator. Use of thepresent invention will eliminate the need for safety elements and willeliminate costly engine failures caused by element fractures or otherdust leaks.

What is claimed is:

1. Apparatus for detecting abnormal amounts of foreign material in theair downstream from an air cleaner, comprising:

a. separate air filter means;

b. circuit means for circulating a portion of the air downstream fromthe air cleaner through said separate air filter means; and

c. monitoring means for monitoring the resistance to air flow of saidseparate air filter means.

2. The apparatus of claim 1 wherein said circuit means comprises a probemounted in an air duct downstream from said air cleaner, inlet tubingconnected between said probe and said separate air filter means, andoutlet tubing connected between said separate air filter means and aregion of air pressure lower than the air pressure in said air duct, tocirculate said portion of air through said separate air filter Theapparatus of claim 2 including a venturi having a throat portion, asource of air under pressure for passage therethrough, said throatportion providing said region of lower air pressure, said outlet tubingbeing connected to said throat portion.

4. The apparatus of claim 2 wherein the elements thereof are sized suchthat the velocity of the air portion passing through said probe is lessthan the velocity of the air passing through said air duct in thevicinity of said probe.

5. The apparatus of claim 1 wherein said monitoring means comprisesdifferential pressure sensing means connected across said separate airfilter means, and means responsive to said differential pressure sensingmeans for providing an output signal indicative of the pressure dropacross said separate air filter means.

6. The apparatus of claim 1 wherein said monitoring means comprises apneumatic bridge circuit having said separate air filter means forming apart of one leg thereof, and pressure responsive means mounted acrosssaid bridge circuit responsive to a predetermined change in the balancethereof.

7. The apparatus of claim 6 wherein said bridge circuit has a first legcomprising a pair of known resistor means and a second leg comprisingsaid separate air filter means and another known resistor means, saidpressure responsive means being connected between the center of saidfirst leg and the center of said second leg.

8. The apparatus of claim 7 wherein said bridge circuit is sized so thatunder normal conditions the pressure at the center of said first leg islower than the pressure at the center of said second leg.

9. Apparatus for detecting abnormal amounts of dust in the normallyclean air entering an engine through an air duct connecting an aircleaner and the air intake of said engine, comprising:

a. a small detector filter having a service life under normal clean airflow conditions of at least as long as that of the air cleaner;

b. means including a probe mounted in the air duct for continuouslycirculating a sample of the air therein through said detector filter;and

c. means for indicating a predetermined rise in the pressure drop acrosssaid detector filter.

10. The apparatus of claim 9 wherein the elements thereof are sized suchthat the velocity of the air sample passing through said probe is lessthan the velocity of the air passing through said air duct in thevicinity of said probe.

11. A method of detecting abnormal amounts of dust in the normally cleanair downstream from an air cleaner, comprising the steps of:

a. continuously circulating a portion of said normally clean air througha detector filter; and b. monitoring the resistance to air flow of saiddetector filter to detect an abnormal increase in said resistance as anindication of abnormal amounts of dust in the air.

1. Apparatus for detecting abnormal amounts of foreign material in theair downstream from an air cleaner, comprising: a. separate air filtermeans; b. circuit means for circulating a portion of the air downstreamfrom the air cleaner through said separate air filter means; and c.monitoring means for monitoring the resistance to air flow of saidseparate air filter means.
 2. The apparatus of claim 1 wherein saidcircuit means comprises a probe mounted in an air duct downstream fromsaid air cleaner, inlet tubing connected between said probe and saidseparate air filter means, and outlet tubing connected between saidseparate air filter means and a region of air pressure lower than theair pressure in said air duct, to circulate said portion of air throughsaid separate air filter means.
 3. The apparatus of claim 2 including aventuri having a throat portion, a source of air under pressure forpassage therethrough, said throat portion providing said region of lowerair pressure, said outlet tubing being connected to said throat portion.4. The apparatus of claim 2 wherein the elements thereof are sized suchthat the velocity of the air portion passing through said probe is lessthan the velocity of the air passing through said air duct in thevicinity of said probe.
 5. The apparatus of claim 1 wherein saidmonitoring means comprises differential pressure sensing means connectedacross said separate air filter means, and means responsive to saiddifferential pressure sensing means for providing an output signalindicative of the pressure drop across said separate air filter means.6. The apparatus of claim 1 wherein said monitoring means comprises apneumatic bridge circuit having said separate air filter means forming apart of one leg thereof, and pressure responsive means mounted acrosssaid bridge circuit responsive to a predetermined change in the balancethereof.
 7. The apparatus of claim 6 wherein said bridge circuit has afirst leg comprising a pair of known resistor means and a second legcomprising said separate air filter means and another known resistormeans, said pressure responsive means being connected between the centerof said first leg and the center of said second leg.
 8. The apparatus ofclaim 7 wherein said bridge circuit is sized so that under normalconditions the pressure at the center of said first leg is lower thanthe pressure at the center of said second leg.
 9. Apparatus fordetecting abnormal amounts of dust in the normally clean air entering anengine through an air duct connecting an air cleaner and the air intakeof said engine, comprising: a. a small detector filter having a servicelife under normal clean air flow conditions of at least as long as thatof the air cleaner; b. means including a probe mounted in the air ductfor continuously circulating a sample of the air therein through saiddetector filter; and c. means for indicating a predetermined rise in thepressure drop across said detector filter.
 10. The apparatus of claim 9wherein the elements thereof are sized such that the velocity of the airsample passing through said probe is less than the velocity of the airpassing through said air duct in the vicinity of said probe.
 11. Amethod of detecting abnormal amounts of dust in the normally clean airdownstream from an air cleaner, comprising the steps of: a. continuouslycirculating a portion of said normally clean air through a detectorfilter; and b. monitoring the resistance to air flow of said detectorfilter to detect an abnormal increase in said resistance as anindication of abnormal amounts of dust in the air.